Resistor unit and method of forming the same



Feb. 16, 1932. L. E, PowER RBSISTOR UNIT AND METHOD 0F FORMING THE SAIE Filed June 8. 1927 Patented Feb. 16, 1932 UNITED STATES PATENT OFFICE LAURENCE E. POWER, F MILWAUKEE, WISCONSIN, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO ALLEN-BRADLEY COMPANY, 0F MILWAUKEE, WISCONSIN, A CORPORA- TION OF WISCONSIN Rnsrs'ron UNIT AND METHOD 0F roRivrING THE SAME Application filed .Tune 8, 1927. Serial No. 197,367.

This invention relates to certain new and useful improvements in resistor units and method of forming the same and refers especially to units designed for use in radio receiver circuits and the like.

It is highly desirable that resistor units utilized in radio receiver circuits and the like have a predetermined resistance value, depending upon t-he particular circuit, which value must be substantially correct within a slight latitude and heretofore it has been impossible to produce units ot predetermined resistance values with any degree of accuracy except by adjusting them in the manner illustrated in the copending application oi' Lynde Bradley, Serial No. 53,570.

However, this manner of producing resistor units, while efficient, is objectionable in that it involves considerable handling of the units and the attendant labor expense, and, therefore, it is an object of this invention to provide an improved method of producing resistor units whereby the units may be made in quantities having a predetermined resistance value without requiring unnecessary handling of the units.

Another object of this invention resides in the provision of an improved method of forming resistor units in which the ingredients are such as to permit the production of resistance units of predetermined value by controlling the proportions of the ingredients, wherebythe necessity of adjusting the units after formation is eliminated.

Another object of this invention resides in the provision of an improved resistor unit having a carbon black, such as gas black or lamp black, incorporated therein as a conductor togetherl with asbestos ibre and clay or the like, as a filler, and a phenol condensation product as a binder.

A further object of this invention resides -in the provision of an improved method of forming resistor units having a predetermined resistance value which consists in thoroughly mixing gas or lamp black with a filler including asbestos and a binder, preferably phenol resin, reducing the mixed'ingredients to a powder, blending stock powders with the mixture to increase or decrease the percentages of conductivity of the materials Vto thus produce predetermined conductivit-ies and 'forming the blended powder into the iinishcd units.

It is a still further object of this invention to provide an improved method of forming resistor units by iirst molding the ingredients sufiicient for one unit into a slug or bar and in forming the unit from the slug or bar.

W'ith the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of part-s substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims,

In the accompanying drawings, I have illustrated one complete example of the physical embodiment ot my invention constructed according to the best mode I have so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a side elevational view of the slug or bar into which the ingredients of a resistor are initially formed;

Figure 2 is a vertical sectional view through a forming mold illustrating the molding of the slug to form the finished unit, and

Figure 3V is a side elevational View of a completed resistor unit.

Referring to the drawings, the numeral 5 designates a complete resistor unit having a body 6 composed of a conductor, a iiller and a binder, as 'later described, and provided with end cap or terminal members 7, the terminal members 7 providing means for mounting the unit within an electrical circuit, not shown. .v

In radio circuits, it is of utmost importance that the units have definite resistance values and great diiiicult has been experienced in obtaining any de nite value, the most successful method now in use being that described in the copending application referred to. The method of setting or adjusting the resistance value of the units by shooting, i. e., subjecting them to the iniiuence of an electricalcurrent h-aving the capacity to reous objection that the unit must be handled considerably in manufacture, thus adding to the labor cost. This objectionable feature is overcome and a resistance unit of any desired resistance value is produced by controlling the proportions of the ingredients entering therein.

It has been found from practice that the following mixtures when molded into a resistance unit produce units of the values noted: 1

Resistor' units of approximately one million (1,000,000) ohms:

Conductor, such as gas or lamp black 25% Filler, such as asbestos fibre and clay 28% Binder, such as a phenol `condensation product 47% Resistance units of approximately forty million (40,000,000) ohms:

Conductor, such as gas or lamp black` 18% Filler, such as asbestos fibre or asbestos fibre and clay 37% Binder, such as phenol condensation product 45% The above are merely examples of the combinations used and should it be desired to obtain values other than those mentioned above, the mixtures are planned accordingly.

To produce a batch of mixture for resistance units, phenol resin is first made from phenol formaldehyde, ammonia, etc. which is cured to a point where it is hard at the ordinary room temperature and soft when heated. This hardened phenol resin is then ground to a powder and the other materials such as fillers and conductors are mixed therewith in a ball mill.

The ingredients are then further mixed hot on rollers, such as rubber calenders, the heat being obtained by the dissipation of energy in rolling, the resultant product being a sheet of the commingled ingredients.

v The sheet is then broken up and ground to a powder, which forms the base for the resistance units and the proportion of ingredients thereof produces a unit of the maximuni resistance value, and assuming the pounds per square inch at a temperature of i four hundred degrees (400) Fahrenheit. The units are then complete and the end terminals or caps 7 are pressed on the ends to provide means for incorporating the units Within an electrical circuit and it will be. apparent that the end terminals may be dispensed with, if desired as illustrated in my copending application erial No. 197,882.

u From the foregoing description taken in connection with the accompanying drawings, it Will be readily apparent to those skilled in the art to which an invention of the character described appertains that provide a novel and improved resistor unit and method of forming the same which is capable of production ata lower cost and which is very efficient in operation.

What I claim as my invention is:

l. A resistor unit having approximately one million ohms capacity, consisting of approximately twenty-five per cent carbon black, approximately fourteen per cent asbestos fibre, approximately fourteen per cent clay, and approximately forty-seven per cent phenol condensation product.

2. The hereindescribed method of forming a resistor unit which consists in thoroughly commingling carbon black, asbestos fibre and a phenol condensation product, in preforming the ingredients into a stick capable of maintaining its own form, and in finally forming the unit from the stick.

In testimony whereof I' have hereunto affixed my signature.

LAURENCE E. POWER.

maximum resistance desired is forty million ohms, the proportions are as mentioned above in the second example. This stock mixture is then further blended with other mixtures of the same ingredients to vary the propore tions according to the conductivities required, the blended mixture being formedv into sticks or slugs 8, preferably by an automatic tablet machine, not shown.

Each stick or slug is then placed in a mold 9 and subjected to a pressure ofroughly 160 tonsper square inch, through a plunger or pin 10. The units are then baked or treated under an air pressure of roughly two hundredl 

